There's going to be a couple spoilers in here, just as a heads up.

Been playing this game for a bit now and noticed in two quests that the NPCs I have a potential to protect are almost impossible to do.

Specifically I will mention 'Little Sisters' and something close to 'Blood Curse' where you have to escort the soldiers through a group of drowners. Maverick died within a few hits before I could really start fighting the Sisters. I reloaded this save countless times to try various traps, stuns, but nothing worked. He just died far too easily.
On the quest to escort the soldiers I resorted to a walkthrough where the player ran towards the furthest 3 drowners and left the soldiers to fight the others behind him. However, by the time he had killed 3 he was still able to kill the rest but after I kill a single one at least one of the soldiers has died.

Would Full Combat Rebalance 2 cause this?

I play with FCR in both W1 and W2, and didn't have any trouble with the escort missions.
Perhaps hold off on the difficult quests until you've done more character development, and use the most appropriate weapon (usually silver) and oils. You could also try bombs (though I didn't use them). They are reported to be *very* powerful if your character is a bit weaker.

Maybe consider building/finding/buying better swords if you haven't got great ones... IIRC I was still using the Rune Sihil and a Witcher's Silver Sword built from the combination that gives 3 rune slots.

I tried to take your advice on board and ended up in the same situation. I only have the first Witcher's Silver Sword and Devil. I found 3 other diagrams for Silver Swords which all had the same damage of 17. I applied oils to boost maximum sword damage and resorted to lighter armour to lessen the damage penalty.

I recorded a video, which I could not upload due to poor uni internet, but I timed the first NPC's death at 5 seconds, perhaps even 4, after combat began. I cannot defend them! I stunned one of the drowners with Yrden and knocked one over with Aard but they still are killing these guys in a few hits. The same is happening to Maverick with Little Sisters. I honestly mean it is a matter of seconds!

Edit: I even resorted to grouping them up and using 2 grapeshots, which killed them, but then all of them respawned immediately!
Edit2: I managed to pick most of them off with just my sword but they still respawned. Is this right? I'm on normal difficulty and my friends are telling me this has never happened to them.

Deleted (because reference post has been deleted).